I noticed a few weeks ago that my heater was dripping water from the bottom on the side the pipes come in to it. When the heater is operating, the leak stops, which tells me this is from something expanding and plugging the leak or that the leaking water is simply evaporating on a hot surface. I tend to suspect the first possibility since the leak returns quite awhile after the heater shuts off. Is this typical of a bad heat exchanger or likely something else?